Lab Report: Fundamental Laboratory Techniques

Categories: Chemistry

Report, Pages 10 (2377 words)

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I. Abstract

In this laboratory experiment, students gained valuable experience in mastering fundamental techniques required for successful experimental work. The objectives included familiarization with common glassware and their proper usage, precise weighing on an analytical balance, basic statistical analysis for expressing results (calculating mean, standard deviation, % RSD), identifying outliers, preparation of aqueous standard solutions, accurate aliquot delivery, and dilution procedures.

II. Introduction

Before undertaking complex tasks in the laboratory, it is essential to acquire a solid foundation in fundamental laboratory skills.

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Proficiency in these skills is crucial not only for producing accurate and reproducible experimental results but also for preventing damage to expensive equipment and ensuring a safe laboratory environment for all participants. This experiment serves as a foundational step in gaining knowledge and understanding of commonly used laboratory glassware and their functions.

III. Experimental Procedure

A. List of Chemicals

NaCl powder
Distilled water
5 pieces of 5-peso coin
Analytical balance
Reagent bottles, 100mL
Beaker, 150 mL
Volumetric flasks with stopper, 100mL
Serological pipette with rubber stopper, 10mL

B. Procedure

The experimental procedure was conducted in several steps:

Collecting and Weighing Samples

First, five 5-peso coins were selected as samples. Prior to weighing, it was ensured that the analytical balance was properly calibrated and cleaned. The samples were then carefully weighed, and the results were recorded with precision to four decimal places. Subsequently, using the obtained sample data, calculations were performed to determine the mean, standard deviation, and relative standard deviation (% RSD).

Weighing Solid Samples (NaCl)

For solid samples such as NaCl powder, an improvised weighing method was employed using aluminum foil.

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Before placing the NaCl powder into the analytical balance, the TARE function was used to zero the balance. The NaCl powder was cautiously added using a spatula until a mass of 0.400 g was obtained, with a tolerance not exceeding 0.0030 g. The weighed NaCl powder was then transferred to a 150-mL beaker.

Preparing NaCl Solution

The weighed NaCl powder was dissolved in approximately 10 mL of distilled water while stirring the solution with a stirring rod. Subsequently, the partially dissolved NaCl powder was transferred to a 100-mL volumetric flask. This process was repeated until no residue remained in the beaker, and the solution level reached the mark on the volumetric flask. The last traces of the solution adhering to the stirring rod were rinsed into the volumetric flask using a wash bottle and Pasteur pipette. The solution was further diluted until the bottom of the meniscus aligned with the graduation mark on the flask. A stopper was placed on the volumetric flask, and the solution was mixed thoroughly. Before calculating the concentration of the solution, it was transferred to a reagent bottle and appropriately labeled.

Aliquot Transfer and Dilution

Using a serological pipette, a 10-mL aliquot of the previously prepared NaCl solution was transferred to a 100-mL volumetric flask. Distilled water was added to the flask to reach the mark, and a stopper was applied. The solution was mixed thoroughly before being transferred to a reagent bottle and labeled appropriately.

IV. Data

Table 1. Analytical Balance Measurements and Statistical Analysis

Parameter	Value
Mean (g)	7.4525
Standard Deviation	0.4148
% RSD	5.5659%

Table 1 displays the results of measurements taken using an analytical balance and the subsequent statistical analysis. The data obtained from weighing five samples of 5-peso coins on the analytical balance yielded the following results: a mean of 7.4525 g, a standard deviation of 0.4148, and a relative standard deviation (% RSD) of 5.5659%.

Table 2. Weight of NaCl

Parameter	Value (g)
Weight of NaCl	0.3981

Table 2 reports the weight of NaCl, which was measured to be 0.3981 grams using the analytical balance.

Table 3. Computed Molarity of NaCl Solution

Parameter	Molarity
Molarity of NaCl solution	0.006812

Table 3 provides the computed molarity of the NaCl solution, which was determined to be 0.006812.

Table 4. Molarity of NaCl Solution in Aliquot Delivery

Parameter	Molarity
Molarity of NaCl solution (in aliquot delivery)	0.0006812

Table 4 presents the calculated molarity of the NaCl solution specifically for aliquot delivery, which was determined to be 0.0006812.

V. Discussion

Function of TARE Button in an Analytical Balance

The TARE function on an analytical balance is used to reset the digital display to zero when pressed. This function is essential because it allows the mass of the sample to be read directly without including the mass of the container or any other objects used for weighing.

Other Types of Balances Found in the Laboratory

Various types of balances can be found in laboratories, each designed for specific applications:

Platform Scale: This scale is equipped with a load-bearing platform for weighing heavy objects. The weight is transmitted to a beam that can be balanced by adjusting a counterpoise, which counterbalances the weight on the platform.
Top-Loading Balance: These balances are suitable for measuring objects weighing approximately 150–5000 g. While they offer less precision compared to analytical balances, they provide a quick and convenient solution for measurements that do not require extreme accuracy.
Equal Arm Balance/Trip Balance: This type of laboratory scale features two pans on opposite sides of a lever. It can be used in two ways: by placing the object to be weighed on one pan and adding standard weights to the other until balance is achieved, or by using it as a triple-beam balance to directly measure an object's mass based on the positions of the beams.
Spring Balance: Spring balances measure the weight of an object by opposing the force of gravity with the force exerted by an extended spring. They are commonly used for everyday measurements.
Torsion Balance: Torsion balances operate based on the amount of twisting of a wire or fiber. Many microbalances and ultra-microbalances, designed for weighing fractional gram values, utilize torsion principles for their measurements.
Triple-Beam Balance: The triple-beam balance is used for precise mass measurements, with a reading error of 0.05 gram. The differing sizes of the beams indicate varying weights, and each beam corresponds to a specific reading scale.

VI. Proper Uses of Laboratory Glassware

Pipette

A pipette is a precise instrument used for measuring and transferring liquids. Different types of pipettes exist, such as serological and volumetric pipettes, each with specific purposes and usage guidelines:

Volumetric Pipette: Volumetric pipettes are calibrated to have a high level of accuracy. The numbers and lines or marks on the pipette indicate the volume it holds or dispenses when filled to the mark. When using a volumetric pipette, you can report the volume with up to two figures after the decimal point for increased precision. To use a volumetric pipette, follow these steps:
1. Fill the pipette with the liquid using a rubber bulb, ensuring the tip remains submerged in the liquid.
2. Allow the fluid level to rise slightly above the mark on the pipette.
3. Remove the bulb and quickly seal the top of the pipette with your finger.
4. Release a small amount of air to drain the excess liquid until the bottom of the meniscus aligns with the mark.
5. Transfer the liquid to the receiving container, rinse the pipette for future use.

Volumetric Flask

Volumetric flasks are used for precise preparation of standard solutions. Follow these steps when using a volumetric flask:

Select an appropriately sized flask for your procedure.
Calculate and measure the mass of solid material needed for the desired solution.
Transfer the material into the flask, using a funnel to avoid any loss during transfer.
Rinse the funnel sides with solvent to capture residual material adhering to it.
Fill the flask halfway with the solvent, cap it, and swirl to dissolve the solid material into the solution.
Once the solid material is fully dissolved, fill the flask almost to the etched line.
Add solvent carefully with a medicine dropper to raise the base of the meniscus to the etched line.
Cap the flask, mix, swirl, and store the prepared solution for future use.

Beaker

Beakers are versatile containers used for various laboratory purposes. To use a beaker, follow these guidelines:

Pour the liquid into the beaker slowly to prevent splashing.
Use the measuring lines on the beaker to estimate the liquid volume.
Stir the liquid with a stirrer if necessary.
When heating, do not fill the beaker more than one-third to avoid spills.
Handle hot beakers with safety tongs.
Pour liquid out of the beaker using the spout in the lip around the top.

Filter Funnel

A filter funnel is used to separate solids from liquids. Follow these steps when using a filter funnel:

Place a cone-shaped filter paper inside the funnel.
Pour the suspension of solid and liquid through the funnel.
Large solid particles will be retained on the filter paper, while smaller liquid molecules pass through, creating a filtrate.
Dispose of the used filter paper if only the liquid is of interest.
Clean reusable screens, such as those made of polyethylene or galvanized steel, to filter debris from automotive and workshop fluids.

Reagent Bottle

Reagent bottles are used to store chemicals safely. Follow these steps when handling reagent bottles:

Select an appropriately sized beaker and label it.
Hold the stopper during transfer or, if flat, place it upside down on the counter.
Carefully pour the required amount of reagent into the beaker.
Avoid excess pouring.
Close the reagent bottle securely after use.

Weighing Bottle

Weighing bottles are used for precise measurement of solids. Follow these guidelines when using weighing bottles:

The amount of material to transfer may require several attempts for precision.
Do not attempt to transfer excess solid material back into the weighing bottle.
If overshooting occurs, discard the solid material properly, rinse the vessel, and start the process again.
Use the appropriate amount of transferred reagent as a visual guide for subsequent samples.

Differences between Serological and Volumetric Pipettes

Serological and volumetric pipettes serve distinct purposes and exhibit differences:

Serological Pipettes: These pipettes have graduated volumetric markings and are designed to deliver various volumes with an accuracy of +/- 0.5-1.0%. They are versatile for transferring different volumes as needed.
Volumetric Pipettes: Volumetric pipettes are calibrated to deliver a specific fixed liquid volume with free drainage. They are available in sizes ranging from 0.5–200 mL and offer higher accuracy and precision but are limited to a single volume measurement.

Additionally, serological pipettes may allow subsequent blowing, while volumetric pipettes do not permit further manipulation after filling.

VII. Uses, Advantages, and Limitations of Glass vs. Plastic Volumetric Pipettes

Use of Glass Pipette: Glass pipettes are employed for their high precision in dispensing liquids, primarily in the preparation of solutions within volumetric flasks. Glass pipettes feature etched marks denoting precise volumes, and the solution is drawn into the pipette using a pipette bulb, never by mouth.

Advantages of Glass Pipette:

High clarity enables content visibility and accurate volume recording.
Sealed glass containers are impermeable to atmospheric gases, preventing oxidative degradation of contents.
Glass is inert and does not contribute to leaching contamination, except for some ionic species.
Glassware is reusable after proper cleaning.
Glass items are easily sterilized compared to plastic items.
Glassware fabrication is possible in laboratories using the services of a glass blower, unlike plastic ware.
Glass beakers and flasks can be safely heated using hot plates.

Limitations of Glass Pipette:

The primary drawback of glassware is its susceptibility to breakage, resulting in loss of samples, potential spillage of harmful substances, and injuries.
Contamination of stored samples due to leaching of inorganic ions or exposure to light in the case of light-sensitive materials.
Unsuitable for handling hydrofluoric acid, which readily attacks glass.

Use of Plastic Pipette: Plastic pipettes have enhanced convenience and handling capabilities for laboratory samples, contributing to options available to laboratory chemists.

Advantages of Plastic Pipette:

Non-breakable and offers some flexibility.
Lightweight, making it easier to handle large items such as desiccators or graduated cylinders.
Non-leaching of inorganic species, making plastic containers preferable for trace metal studies (not suitable for most organic solvents).
Plastic items like vials and micro pipette tips are often disposable but can be reused after proper cleaning to reduce environmental impact.
Generally less expensive compared to glass items.

Limitations of Plastic Pipette:

Lower clarity compared to glass.
Less tolerance to high temperatures.
Graduation marks may not be as clear, leading to potential inaccuracies.

The selection of appropriate labware should consider specific analysis requirements, with plastic labware offering advantages for some applications while others necessitate the use of glass labware. Understanding the properties of different plastic materials available for laboratory use can help in making informed choices.

VIII. Reasons for Not Returning Unused Chemicals to Their Respective Reagent Bottles

Unused reagents should not be returned to their original containers to prevent contamination of the reagent in the original bottle. Once a reagent is exposed to the laboratory environment, it may become impure or undergo changes in its chemical properties due to exposure to the atmosphere or other laboratory conditions after being removed from its original container. Returning unused chemicals to the reagent bottles poses several risks:

Contamination of the entire contents of the stock bottle.
Loss of stability of stored material.
Potential leaching of inorganic ions into aqueous solutions.
Exposure to light, affecting light-sensitive materials.
Risk of introducing impurities or foreign substances.

Unused chemicals should be disposed of according to prescribed waste disposal instructions, ensuring proper handling and disposal procedures are followed to maintain laboratory safety and prevent contamination.

IX. Aliquot and Dilution

An aliquot is a sub-sample extracted from an original sample, representing a fractional part of the whole sample. It is typically used for analysis or further experimentation. Aliquoting allows for more precise measurements and ensures representative sampling.

Dilution involves the addition of a solvent to a solution, reducing the concentration of the solute. This process is commonly used to adjust the concentration of a solution to a desired level. Dilution can be performed using volumetric glassware and is a crucial technique in many laboratory procedures.

X. Conclusion and Recommendations

Based on the experimental results, it is evident that lower %RSD values indicate a more precise measurement, while higher %RSD values indicate less precision. Furthermore, a higher molarity corresponds to a greater amount of NaCl dissolved in distilled water, resulting in a less clear solution, whereas a lower molarity indicates a clearer solution with less NaCl dissolved.

It is recommended that materials be adequately prepared to facilitate accurate measurements, and rushing through the measurement process should be avoided to maintain precision. Proper calibration of measuring equipment is highly advised to minimize errors and ensure reliable results in laboratory experiments.

Lab Report: Fundamental Laboratory Techniques. (2024, Jan 06). Retrieved from https://studymoose.com/document/lab-report-fundamental-laboratory-techniques